[R-sig-ME] Syntax for adding group-level predictors

[Thierry Onkelinx]

Dear Yashree,

You added "Age" to the fixed effects. This assumes that the slope of
Age is shared among all household. Which makes sense to me.

For "Size" you have two options: Size + Age + (1|ID) or Age + (1 +
Size|ID). The former assumes that the slope of Size is the same for
each household (hence a 'fixed' slope). The latter assumes that each
household has a different slope for Size (hence a 'random' slope).

Best regards,

ir. Thierry Onkelinx
Statisticus / Statistician

Vlaamse Overheid / Government of Flanders
INSTITUUT VOOR NATUUR- EN BOSONDERZOEK / RESEARCH INSTITUTE FOR NATURE
AND FOREST
Team Biometrie & Kwaliteitszorg / Team Biometrics & Quality Assurance
thierry.onkelinx at inbo.be
Havenlaan 88 bus 73, 1000 Brussel
www.inbo.be

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2018-05-11 14:50 GMT+02:00 Yashree Mehta <yashree19 at gmail.com>:
> Hi,
> I am working with a random intercept model. I have the usual "X" vector of
> covariates and one id variable which will make up the random intercept. Now
> I wish to add group-level predictors (which are NOT in the X vector) such
> that the random intercept depends on these predictors.
> For example,
> Response variable: Production of maize
> Covariate: Size of plot
> Group-level predictor: Age of farmer
> ID variable: Household_ID
>
> I wish to confirm the syntax for including the group-level "Age of farmer"
> variable.
> fit<-lmer(Production~ Size+ Age+ (1|Household_ID), data=data)
>
> Is this correct or is there another way of declaring the group-level
> predictor in the formula?
>
> Thank you
>
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>
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